Circuit theory of paralleling switching converters

This paper studies the various paralleling styles for dc-dc switching converters from a circuit theoretic viewpoint. The study begins with a systematic classification of the types of parallel-connected dc-dc converters. In the classification, converters are modeled as current sources or voltage sources. From Kirchhoff's laws, the possible connection styles for paralleling current sources and voltage sources are derived, leading to the identification of three types of configurations for paralleling dc-dc converters. Then, control arrangements are classified according to the presence of current-sharing and voltage-regulation loops. Moreover, detailed operating principles with and without a current-sharing loop for the three basic paralleling connections to obtain both current sharing and voltage regulation are given. Applying small-signal analysis to the practical circuits, the inherent characteristics of each scheme are expounded. The roles of the current-sharing loop and origins of current-sharing errors are highlighted. Characteristics for all the schemes are obtained in terms of their performances in current sharing and voltage regulation. Finally, an experiment prototype is built to validate the analysis. The results clearly show the properties of the various paralleling schemes.